The reaction of phenol with formaldehyde are well known in the art. Basically there are two types of phenolic resins -- the resoles and the novolacs formed by basic and acidic catalysis, respectively. When the phenol-formaldehyde reaction is catalyzed with a base, and the mixture contains one or more than one mole of formaldehyde per mole of phenol, the result is a one step resin, called a resole. This reaction can be summarized by the following equations: ##STR1##
Such mixture of phenolic alcohols are widely known and used, and are referred to as "resoles". Upon further heating these alcohols, the "resoles" tend to polymerize to form a phenolic resin.
On the other hand, the result of an acid catalyzed reaction of less than one mole of aldehyde per mole of phenol is a "novolac" resin, of the following formula: ##STR2## wherein the resin is a mixture of such molecules, and wherein, in respective molecules, N is zero or an integer. The cure of novolac resins is usually carried out by reaction of the resins with hexamethylenetetraamine. However, resoles can be used to cross link novolacs.
The use of furfuryl alcohol as a polycondensate for both resoles and novolacs is well known, as illustrated by U.S. Pat. No. 3,312,650 issued to Arthur Case and Royden Rinker and U.S. Pat. No. 3,299,167 issued to Paul D. Knowlson and Elliot W. Simpson.
However, the present invention relates to the curing of furan-formaldehyde resins with resoles under acidic conditions. The term "furan-formaldehyde resin" referred to herein are those that may be formed, for example, by the reaction of an alpha-unsubstituted furan, such as furan itself, with formaldehyde as disclosed in U.S. Pat. No. 4,017,461 issued on Apr. 12, 1977, to Andrew P. Dunlop and Rudy F. Macander. They have the following chemical structure: ##STR3## wherein X and Y may be alike or different, and include hydrogen, halogen, alkyl, phenol, alkyl-substituted phenol, halogen substituted phenol, hydroxy alkyl, carboxy alkyl, in which the alkyl substituents have from one to 10 carbons, and wherein R and R' includes hydrogen, or hydroxymethyl. When very large excess of furan is used and upon complete reaction of the available formaldehyde in the Dunlop-Macander reaction referred to above, R and R' are predominantly hydrogen, and wherein N is an integer, at least one. When only a slight excess of furan is used in the Dunlop-Macander reaction, R and R' will include greater amounts of hydroxymethyl termination in the resin. Such resins range in viscosity from about 50 cps to more than 100,000 cps with increasing N value and, typically, with increasing levels of hydroxymethyl. The resins are mixes of molecules having different values of N. We have discovered that in accordance with the present invention these resins couple with phenolic resins of the resole type under acidic catalysis conditions. The acids useful as catalysts in accordance with the present invention, include any strong acid. However, the aromatic sulfonic acids are most preferred for use as catalyst in accordance with the present invention.
The liquid catalyst resole-furan formaldehyde resin reaction mixtures in accordance with the present invention are useful as liquid, hardenable binders for use with glass fibers, foundry sand, etc., in the manufacture of composite articles, for example. When sand or glass-fiber is bound with the liquid resole-furan formaldehyde resin reaction mixtures in accordance with the present invention, it is preferred that a silane be included as an ingredient in the binder mixture.
Silanes useful in accordance with the present invention can be any organo silicon compound referred to in U.S. Pat. No. 3,737,430 to Brown, et al. In addition other specific examples include the following:
gamma-mercaptopropyltrimethoxysilane PA1 N-beta-(aminoethyl)-gamma-aminopropyltrimethoxysilane PA1 beta-(3,4-epoxycyclohexyl)ethyltrimethoxysilane PA1 gamma-glycidoxypropyltrimethoxysilane PA1 gamma-aminopropyltriphenoxysilane PA1 gamma-aminopropyltribenzoxysilane PA1 gamma-aminopropyltrifurfuroxysilane PA1 gamma-aminopropyltri(o-chlorophenoxy)silane PA1 gamma-aminopropyltri(p-chlorophenoxy)silane, and PA1 gamma-aminopropyltri(tetrahydrofurfuroxy)silane PA1 methyl[2-(gamma-triethoxysilypropyl-amino)ethyl amino]3-propionate in methanol PA1 modified amino-organosilane PA1 Ureido-silane PA1 mercaptoethyltriethoxysilane PA1 chloropropyltrimethoxysilane PA1 vinyltrichlorosilane PA1 vinyltriethoxysilane PA1 vinyltrimethoxysilane PA1 gamma-methacryloxypropyltrimethoxysilane PA1 gamma-methacryloxypropyltri(2-methoxyethoxy)-silane PA1 vinyltriacetoxysilane PA1 gamma-aminopropyltriethoxysilane
The list of commercially available and recognized composite article adhesion promoters is lengthening as further research and development continues, and it is expected that any commercially available adhesion promoter is useful to advantage as an ingredient with the resole-furan formaldehyde binder system in accordance with the present invention.
It is contemplated that any phenolic resin of the resole type is useful in accordance with the present invention. We have chosen to describe the use of several commercially available resoles for the purpose of illustrating the invention, and for the purpose of setting forth what presently is regarded as the best mode.
It is also contemplated, that the liquid resin which results from less than completion of the coupling reaction is useful as a binder for producing foundry sand shapes. The examples that follow will also illustrate this contemplated use.
In the following examples all parts are expressed in parts by weight, all temperatures are expressed in degree centigrade, and all percents are expressed in percent by weight based on 100 parts by weight of the material then being referred to.